1. Field of the Invention
The present invention relates to joining, tie-in or fastening of pipelines subsea. More particularly, the present invention relates to joining of pipelines subsea, or tie-in of a pipeline subsea, by use of diverless welding. Diverless welding means in this context that there is no need for the aid of divers for preparation, installation of equipment, welding or demobilization of equipment. With the invention, a remote-controlled diverless joining system for subsea pipelines is provided.
2. Description of the Related Art
For the time being, joining of subsea pipelines very often requires work performed by divers. From 31 Dec. 2004 it is planned for Norwegian waters to limit the maximum allowable working depths for divers to 250 meters for emergency operations, up from the earlier limit of 360 meters. For pipelines having outer dimensions of 8″ to 22″ there are diverless systems for applying an external sleeve to connect pipelines that are to be joined. More particularly, MORGRIP 3000R mechanical coupling, which is installed without welding, is available from Hydrotight Sweeny Ltd., West Midlands, England. For pipelines of larger diameter it can often be possible to undertake the welding diverless, but divers must contribute by preparing and installing/demobilizing required equipment, such that the joining system overall is not diverless. In practice, there is no available technology for diverless joining of pipelines having dimensions of 28″ and larger, such as dimensions up to 42″ or even 48″.
For pipelines on and from the Norwegian continental shelf the pipeline repair system PRS is usually utilized. The PRS system is available from the PRS-administration, Haugesund, Norway. The PRS system utilizes automated TIG-welding, but the equipment requires work by divers for installation.
A demand exists for equipment for completely diverless joining of pipelines at depths or more than 250 m for dimensions larger than 28″. The objective of the present invention is to meet the demand.
The closest prior art to the present invention is constituted by the above-mentioned PRS system, and the above-mentioned MORGRIP-couplings. Relevant background art is described in the patent publications U.S. Pat. No. 6,131,801, NO-B-159,307, U.S. Pat. No. 5,437,517, GB-A-2323907, GB-A-2304394, NO-BI-304753, NO-BI-304954 and NO-B1-149288.